The present invention relates to a pneumatic tire having less heel and toe wear around lateral tread grooves.
Various types of tread patterns have been used for a pneumatic tire, for examples, a rib type pattern consisting of main grooves extending circumferentially of the tire in a straight or zigzag configuration, a rib-lug type pattern consisting of main grooves and axially extending lateral grooves formed in the shoulder regions of the tire, a tread pattern called all-season type or snow type consisting of main grooves and lateral grooves crossing the main groove, a lug type pattern consisting of wide lateral grooves extending to the equator of the tire from each tread edge, a block type pattern consisting of wide main grooves and wide lateral grooves intersecting the wide main grooves, and the like.
In a tire provided with lateral grooves on the tread like the above-mentioned rib-lug type or all season type patterns, its performance such as traction, wet grip and the like is improved by such lateral grooves. Such lateral grooves, however, shorten the wear life of the tire.
As shown in FIG. 21, the tread face T wears partially at radially outward portions of the groove sidewalls GW of the lateral groove G, and the wear K of the portion on the kick-out side Ga (the toe side) is faster and greater than that on the other step-in side (the heel side), and accompanying with the wear K the wear of the portion on the step-in side grows to a so-called heel and toe wear, whereby the wear life is shortened.
In order to prevent such abnormal wear, there have been proposed to increase the hardness of the rubber for the sidewalls of the lateral grooves, to decrease partly the groove depth of the lateral grooves, to increase the inclination angle of the sidewalls of the lateral groove, to and decrease the groove width and the like, which are intended to improve the resistance to wear or to lessen the amount of the slip of the tread against the road face by lessening the movement of the groove sidewalls GW into the lateral groove G.
However, to use the harder rubber for the sidewalls of the lateral groove complicates the production of the tire, and such rubber partly increases the hardness at the tread face, which sometimes degrades tire performance such as road traction. Further, the decreased depth of the lateral grooves tends to decrease traction in on-the-snow performance and wet grip. Also by increasing the inclination angle of the groove sidewall and decreasing the groove width, a substantial improvement in preventing uneven wear can not be expected.
It is therefore, an object of the present invention to provide a pneumatic tire in which uneven wear of the tread is prevented and tire life is prolonged by bridging the lateral grooves disposed in the tire treat.